Preparation of halides of plutonium



nite States v 2,851,332 Patented Sept. 9, 1958 PREPARATION OF HALIDES FPLUTONIUM Clifford S. Garner, Los Angeles, Calif., and Iral B. Johns,

Payton, Ohio, assignors to the United States of Amerrca as representedby the United States Atomic Energy Commission No Drawing. ApplicationApril 21, 1950 Serial No. 157,398 11 Claims. (Cl. 23-145) This inventionrelates to metal halides and more particularly, to methods for preparingsaid metal halides. Specifically, this invention is directed to thepreparation of plutonium metal halides by dry chemistry methods.

In the past it has been necessary to employ several processes forconverting the slurry of plutonium nitrate obtained by dissolving thefuel elements from a neutronic reactor to a form which is moreconveniently processed as, for example, the oxalate or the oxide.Additional dry chemical processes have then been used to convert theoxide or oxalate to a readily reducible compound such as the halide ofthe metal. The details and operation of the dry chemical processes areset forth fully in copending patent applications S. N. 753,568, filedJune 9, 1947, by Clifford S. Garner for Dry Chemical Methods which setsforth a method for the conversion of plutonium oxalate to plutoniumhalides, and S. N. 753,569, filed June 9, 1947, by Clifford S. Garnerfor Production of Metal Compounds which discloses a method for the drychemical conversion of plutonium oxalate to the oxide. Also, copendingapplication S. N. 753,567,filed June 9, 1947, by Norman A. Davison andJoseph J. Katz, entitled Method For the Preparation of Plutonium Halidesand Oxyhalides, specifically discloses the formation of plutoniumfluoride by the dry chemistry treatment of plutonium oxide, PuO with ahydrohalide in the presence of added hydrogen or other reducing agent.None of the above-cited applications nor any prior known method cites asingle-step process for the direct and efiicient conversion of plutoniumnitrate to plutonium halides. It may be seen that a process forconverting the nitrate directly to the halide is a desirable andvaluable process in the manufacture and production of plutoniummaterials.

It is a primary object of this invention to provide a method forefliciently and directly converting plutonium nitrate to a plutoniumhalide.

A further object of this invention is to provide a method for rapidlyconverting higher valent plutonium nitrate to plutonium halides by drychemistry methods.

It is another object of this invention to provide a method for the drychemistry conversion of plutonium nitrate to plutonium chloride.

' Another object of this invention is to provide a method forconvertingplutonium nitrate to plutonium fluoride.

Still further objects and advantages of the present invention willbecome apparent from the description and examples which follow. v

The objects of this invention are achieved by contacting crystallinehigher valent plutonium nitrate with gaseous hydrohalide at atemperature of at least 400 C.

By higher valent plutonium nitrate is meant plutonium nitrate in eitherthe plus 4 or plus 6 valence state. The latter state is commonlyreferred to as plutonyl nitrate, 2) ah- While the general statementabove is of suflicient scope to describe the operation of the broadclaims to the invention, it is to be understood that considerablerefinement of the process is obtained by control of the conditions underwhich the hydrohalide is admitted. When the vapors, are passed over theplus 6 or plus 4 plutonium nitrate under non-oxidizing conditions, forexample, in the presence of a reducing gas such as hydrogen, thetervalent halide is formed. By adding a small amount of an oxidizinggas, for example, oxygen, it is possible to form the tetrahalide. Theamount of the reducing gas or oxidizing gas admitted with thehydrohalide is a minor proportion, being of the order of from 2 to 10percent by volume.

A further improvement in the quality of the halide formed is obtained ifthe temperature of the plutonium nitrate is raised to about 100 C.before the hydrohalide is introduced. It is believed that when thehydrohalide is introduced at room temperature an oxyhalide is formed,which oxyhalide is converted with difficulty to the desired metal halideand may introduce other problems with respect to the subsequentreduction of the halide to the metal. However, it is important that thetemperature not exceed 150 C. because the nitrate begins to decompose tothe oxide at that point.

In order more clearly to describe and define the invention the followingexamples are presented. Example I shows one embodiment of the inventionfor the conversion of plutonyl nitrate directly to plutoniumtrifluoride.

Example I A slurry of plus 6 plutonium nitrate in nitric acid isevaporated to dryness under a battery of heat lamps in a properlyventilated hood in order to obtain crystalline plus 6 plutonium nitrate.About 25 milligrams of the solid material are weighed out on a tarredplatinum boat which is then placed in a cold mufile furnace under aplatinum canopy and heated slowly in a stream of nitrogen to 125 C. Atthis temperature the flow of the inert gas is turned off and hydrogenfluoride is then admitted into the furnace at the rate of about 20 cubiccentimeters per minute. The temperature of the furnace is increasedrapidly to 500 C. and held there for 30 minutes. Under these conditionsthe plus 6 nitrate is converted to plutonium trifiuo'ride at a yield ofpercent of theoretical.

In the conversion of plutonyl nitrate to the lower valence fluoride asin the foregoing example, it is possible to use pure hydrogen fluoridewithout the addition of any other reducing gas, for the hydrogenfluoride reactant appears to be sufficient to insure a substantiallycomplete reduction of the plutonyl compound. In the case of reducingplus 6 plutonium nitrate to the tetrahalide, however, a small amount ofan oxidizing atmosphere is introduced with the hydrohalide to assurethat the halide will be formed as the higher valence plus 4 compound.

The next example presents this further embodiment of the invention fordirectly converting plutonyl nitrate to plutonium tetrafiuoride.

Example II A hundred milligrams of plus 6 plutonium nitrate crystalsprepared by evaporating a nitric acid solution of plus 6 plutoniumnitrate to dryness are weighed in a platinum boat and the whole placedin a nickel reaction tube. The temperature in the tube is raised toabout C. and a mixture of hydrogen fluoride and oxygen is admitted atthe rate of from 10 to 30 cubic centimeters per minute while thetemperature is increased slowly to about 450 C. and held there for anhour. The amount of oxygen present in the mixture is about 2 percent byvolume, and is suflicient to provide an oxidizing character to thegaseous mixture which permits the plutonyl nitrate to be readily andefiectively converted to the higher valence plutonium tetrafiuoride. Theheat is turned off and the tube and its contents are cooled to about 50C.

before the tube is opened. A fine lavender powder is present in the boatwhich on analysis is found to contain 97 percent plutonium-tetrafluoride by weight.

Plutonium metal nitrates .other: than plutonyl nitrate may heconvertedto the corresponding halide by v.the methodof-this invention.For example, plus 4 plutonium nitrate .may betreated in a manner similarto that disclosed in'the preceding example-to obtain-the plus 4 halide,or, if aslightly more reducing atmosphere isemployed, as by:the additionof 2 to percent'hydrogen, with the hydrogen fluoride, the plus 3 halidemay be obtained. The following example sets forth asatisfactory methodfor 'accomplishing the'conversion of plus'4 plutonium nitrate toplus 3plutoniumchloride.

Example III 250 milligrams of the dry crystalline plus 4 plutoniumnitrate are placed in a platinum dish .and'heated in a reaction tube to110 "C. 'A gaseous mixture comprising 97.5 percent hydrogenchlorideand2.5 percent hydrogen is admitted to-the tube and'the temperature-israised to and held at 475 C. while maintaining theflow ofthe gas atabout 50cubic centimeters per minute. 'After 90 minutes the gas'flow-isstopped and the heat is turned off. The tube is flushed out withnitrogen and cooled, and the blue, powdery plutonium trichloride whichhas formed is removed therefrom.

Other embodiments of the invention are, of course, possible. Forexample, plus 4 plutonium nitrate may be converted to the fluoride andother halides by the method of theinvention. Likewise,-plus-6 plutoniumnitrate may be used to obtain both the triand tetrachlorides. Thefollowing example sets fortha method for preparing plus 4 plutoniumfluoride fromplus- 4-plutonium nitrate on a larger scale.

Example IV One gram of plutonium plus 4 nitrate crystals are spread outon a platinum sheet in a muffle furnace equipped with a gas inlet tubeand outlet. The heat is turned on and the temperature raised to about130 'C. A gaseous mixture comprising 95 percent hydrogen fluoride and 5percent oxygen-is admitted at the rate of about 100 cubic centimetersper minute. The heat is increased rapidly to bring the temperature toabout 550 C. These conditions are maintained for about 2 hours at whichtime the nitrate is substantially .convertedto the higher valentplutonium tetrafluoride.

' Example V sets forth another embodiment whereby plutonyl nitrate isconverted to the trichloride.

Example V 500 milligrams .oiplus: 6 plutonium nitrate crystals areheated to .125" .C. in vacuo for 'minutes in a nickel reaction tube. Thevacuum is broken by admitting a gaseous mixture comprising 90 percenthydrogen chloride and 10 percent hydrogen. The temperature of the'tubeis raised to about 450 C. while the gaseous mixture is passedtherethrough at the rate of 20 cubic centimeters per minute. After 2hours,'the gas flow and heating are stopped, and the reaction productsare cooled. The-solid plutonium trichloride which has formed ispalebluishgreen in color and very pure.

The temperatures employed in the examples whichzare representative ofthe most satisfactory operating temperatures may be varied ratherwidely. In the-reacting step, however, it is desirable to employtemperaturesin the range of at least 400 C. but not above 600 C. and atemperature of about 500 C. is preferable.

It is thus seen that the method of the instant invention provides asimple, single-step process for rapidly .and efliciently convertinghigher valent plutonium nitrates directly to plutonium halides.

While the advantages of the present invention are manifold, and manyembodiments of the invention maybe made without departing from thespirit and scope thereof,

' 4 it is to be understood that this invention is not to be limitedexcept as indicated in the appended claims.

What is claimed is: a

1. A dry chemical method of preparing plutonium halides which comprisescontacting a dry, crystalline higher valent plutonium nitrate with adry. gaseoushydrohalide of the class consisting of hydrogen chloride andhydrogen fluoride at aitemperature of at least 400 C.

2. A dry chemical method -of preparing plutonium halides which comprisescontacting dry, crystallinehigher valent plutoniumnitrate with a gaseoushydrohalide of the class consisting of hydrogen chloride and hydrogenfluoride in the presence .of aminor amount of a reducing gas at atemperature between 400 C. and 600 C.

3. A dry chemical method of preparing plutonium halides which comprisescontacting dry, crystalline higher valent plutoniumnitrate'with agaseoushydrohalide of the class consisting'o'f hydrogen chloride-and hydrogenfluorideadmixed 'with'2 to 10 "percent by'volume of hydrogen at atemperature between 400 'C. and 600 C.

'4.'-A dry chemicalnmethod of preparing plutonium halides-whichcomprises contacting dry, crystalline higher valent plutoniurnnitratewith-a gaseous hydrohalide of the class consisting of-hydrogen chlorideand hydrogen fluoride in the presence 'of a minor-amount of an oxidizing'gas at a'temperature between 400 C. and 600 C.

5. -A- dry chemical method -of preparing plutonium halides whichcomprisescontacting dry, crystalline higher valent plutonium nitratewith a gaseous hydrohalide of the'class "consisting of hydrogen chlorideand hydrogen fluoride admix'ed with2 to 10 percent by volume of oxygenat a'temperature of"between-400 C. and 600 C.

'6. A dry chemical method of preparing plutonium fluoride -whichcomprises contacting dry, crystalline higher valent plutonium 'nitratewith' dry, gaseous hydrogen fluoride at a temperature "between 400 C.and 600C.

7. "A dry chemical method of preparing plutonium fluoride whichcomprises contacting dry, crystalline higher valentiplutonium nitratewith a; gaseous mixture comprising dry hydrogen fluoride and from 2 to10 percent by volume of hydrogenat a temperature between 400 C. and 600"C.

8. A dry"chemical method of preparing plutonium fluoride which comprisescontacting dry crystalline higher valent'plutonium nitrate with agaseous mixture comprising dry gaseous hydrogen fluoride 'and from 2 tol0 percent "by volumeof oxygen'at a temperature between 400 C. and 600C.

9.'A 'dry chemical method of preparing plutonium chloridewhich"comprises "contacting 'dry, crystalline higher valent plutoniumnitrate'with drygaseous hydrogen-chloride at atemperature between 400 C.and 600C.

lOxA dry 'chemical'rnethod of preparing plutonium chloride whichcomprises contacting dry, crystalline higher valent plutoniumnitratewith a gaseous mixture comprising dry hydrogenchloride. and from2 to 10 percent by-volume of' hydrogen at a temperature between 400 C.and 1 '600 7 C.

' 11.'A dry 'che'mical'method' of preparing plutonium chloride whichcomprises contacting dry, crystalline higher valent plutonium nitratewitha gaseous mixture comprising dry hydrogen chloride and from 2to 10percent by volume ofoxygen at a' temperature'between 400 C. and' 600 C.

References Cited'in the file of this patent

1. A DRY CHEMICAL METHOD OF PREPARING PLUTONIUM HALIDES WHICH COMPRISESCONTACTING A DRY, CRYSTALLINE HIGHER VALENT PLUTONIUM NITRATE WITH A DRYGASEOUS HYDROHALIDE OF THE CLASS CONSISTING OF HYDROGEN CHLORIDE ANDHYROGEN FLUORIDE AT A TEMPERATURE OF AT LEAST 400*C.